Elastic fluid turbine bucket wheel



Nov. 12, 1940.

A. R. SMITH Filed Aug. 27, 1958 M WW t His Attorney.

Patented Nov. 12, 1940 UNITED STATES ELASTIC FLUID TURBINE BUCKET WHEEL Arthur R. Smith, Schenectady, N. Y, asslgnor to General Electric Company, a corporation of New York Application August 27., 1938, Serial No. 227,151

6 Claims.

The present invention relates to elastic fluid turbine bucket wheels and more particularly to arrangements for covering and tying together the outer ends of the buckets.

gether by some form of a cover or shroud band attached to the ends of the buckets to confine the operating fluid within the working passage 10 and to prevent it from spilling outwardly past the ends. Because of the relatively great tan-' gential force exerted by the operating fluid against the buckets, particularly in the high pres-. sure stages, a certain amount of bending of the; I individual buckets takes place which is accompanied by a corresponding distortion of the cover between adjacent buckets. the cover together with the centrifugal force due to the wheel rotation, acting outwardly thereon, and the force exerted by the operating fluid acting directly against the surface of the cover severely stresses the attaching means as well as the cover itself. In elastic fluid turbines designed not only for high speed operation but also for modern high pressures and temperatures, the stresses due to the combined forces acting upon the cover are greatly amplified. The usual form of cover consisting of a single tie member has proved incapable of withstanding such. stresses as are imposed upon it during severe operating conditions.

It is an object of this invention to provide a new and improved turbine bucket wheel shrouding arrangement of greatly increased strength that is capable of withstanding extreme operating conditions.

It is a further object of this invention to p roduce a new and improved turbine bucket shrouding arrangement by which the stresses are distributed to the adjacent buckets on both sides of the one being acted upon by the operating fluid while the tying member is secured throughout its length against distortions likely to cause fatigue and failure thereof.

For a consideration of what I believe to be novel and my invention, attention is directed to the following description and the claims appended thereto taken in connection with the accompanying drawing.

In the drawing, Fig. 1 represents a section of a turbine bucket wheel in perspective provided with a cover according to my invention, Fig. 2

is a fragmentary elevation illustrating the manner in which the cover shown in Fig. 1 is assembled, while Figs. 3 and 4 illustrate a second modification of the invention. s

- Referring to Fig. 1 of the drawing, ill indicates the web of the wheel disk or rotor and H the grooved rim thereof which on opposite sides is 50 provided with annular shoulders defining a dove- In turbine bucket wheel construction, adjacent buckets or blades are usually'connectedto- This distortion of tailed portion 12 for retaining the buckets or blades l3 thereon. The bucket bases M are provided with a grooved slot defining an inverted dovetail for cooperatively fitting over the rim of the rotor substantially as shown. This bucket fastening means forms what is commonly termed the inverted dovetail type of fastening and in stood, of course, that the buckets may be se-' 1 cured to the rotor in any other suitable manner. According to my invention, the buckets or blades I3 are each provided with relatively rigid cover portions l5 substantially brid ing the space Y between adjacent buckets at the outer-ends,

thereof. These cover portions prevent the operating fluid fromescaping upwardly past the ends' of the buckets and absorb the force which would otherwise-"bedirected against the shroud band or tying. means; It is preferred that the cover portions are formed integrally with the buckets and be so dimensioned that the. facing surfaces of adjacent covers substantially abut with each other around the periphery of the wheel to "maintain a proper spacing the bucket ends.

Means are also provided for connecting or ty-v ing a group of any suitable number of adjacent buckets together; The outer surfacelof each. cover portion is provided with a circumferm'j tially extending undercut slot' I 6 so located that it 1 I aligns with the adjacent ends of the slots'forrned 1 in the adjacent covers wherebyja continuous on;

cumferential slot is formed adapted to 'remfive' the tying means ll- The oppositeside walls i8 of the slot are provided with'overh'anging portions or beads l9. An integral raised portion or i lug centrally disposed'within the slot of eachbucket cover extends upwardly from the base thereof. of similar metal straps or bars which are provided with aligned notches 23 along their adjoin-- ing edges for cooperatively fitting around the lugs The tying means l1 comprises a pair 20 when they are assembled within the slot It. I

As shown more clearly'in Fig. 2, the straps may v be separately assembled into the slot- It by. first inserting the outer edges thereof under'the overhanging beads l9 as shown at the left in Fig. 2'

and then shifting them so that they lie flat against the base of the slot as shown at the right. After both straps have been assembled in posi- 'tion, they may be secured in place by peening over the edgesof the centrally disposed lugs 20. v

The straps 22 will thereby be forced outwardly against the side walls l8 of the slot. The beads l9 may then be rolled or peened over to securely clamp the outer edges of both straps in place substantially throughout their entire length. e The lugs 20 and the notches 23 are substantially I rectangular in shape so as to any .wedg;

it is seen that the outer ends of the buckets are rigidly secured together against relative movements therebetween. Such relative movements can take place only if relative sliding movements are permitted between the abutting faces of the integral cover portions. Such sliding movements are resisted by the shear strength of the straps 22 fixedly clamped against the surface of the cover portions in the slot "5 as described. By virtue of the integral cover portions I 5, the bucket tying means is not directly stressed by the pressure of the operating fluid passing through the Working passage. Since the tying means is secured against undue stressing and distortion, the possibilities of failure thereof from fatigue are minimized.

In Figs. 3 and 4 is shown a second modification of the invention in which the slot side walls are substantially smooth and perpendicular with respect to the slot base. A single piece tying member or strap 25 may thus be used for tying together a predetermined number of buckets. The strap is suitably perforated for fitting over the lugs 26, which are adapted to be peened, as shown in Fig. 4, to secure the straps in place. The strap is secured against distortions or bending by peening or rolling the extended edges 21 of the slot side walls over the outer edges of the strap substantially as shown in Fig. 4. By beveling the edges of the strap as at 28, a considerable thickness of metal may be rolled over the tying member to amply resist the shearing stresses between adjacent buckets.

Having described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In an elastic fluid turbine having a rotor with buckets mounted on the rim thereof, said buckets being provided with integral cover portions, aligned slots provided in the upper surface of said cover portions, integral portions extending upwardly from the base of said slot of each of said cover portions and spaced from the side walls thereof, means for tying a plurality of adjacent buckets together comprising a pair of bands fitted into said slot on opposite sides of said integral portions, the edges of said side walls and said integral portions peened over the edges of said bands to secure said pair in said slots.

2. In an elastic fluid turbine having a rotor with buckets mounted on the rim thereof, said buckets being provided with individual cover portions integral with the outer ends thereof, a slot pro-' vided in the upper surface of each of said cover portions, the slots of adjacent buckets being so aligned as to provide a continuous circumfer ential slot around the periphery of said buckets, a centrally disposed lug extending upwardly from the base of said slot in each of said cover portions and spaced from the side walls thereof, means for tying a. plurality of adjacent buckets together fitted into said slot and perforated to cooperatively fit around said lugs, the upper edges" of said lugs being deformed to securely fasten said tying means in said slot.

3. In an elastic fiuid turbine having a rotor with a row of buckets mounted on the periphery thereof, said buckets being provided with integral cover portions, the cover portions of adjacent buckets substantially abutting against each other and spacing the outer ends of said buckets apart, means for securing a plurality of adjacent buckets together comprising integral lug portions centrally disposed and projecting upwardly from each of said cover portions, tying means provided with spaced apart perforations for cooperatively fitting around said lugs,jthe edges of said lugs being peened over said tying means, and means for securing the outer edges of said tying means against the surface of said cover portions.

4. In an elastic fluid turbine having a rotor,

. buckets secured to the rim of said rotor, each of said buckets having a cover portion. rigidly connected to the outer end, the cover portions of adjacent buckets abutting with each other to space said buckets apart, the upper surface of said coversbeing slotted so as to provide a continuous circumferential slot around said buckets, a rectangular lug projecting upwardly from the base of said slot and centrally disposed in each cover portion with respect to the side walls of said slot, means for securing a plurality of said buckets together comprising a member perforated so as to cooperatively fit around said lugs and secured in said slot by the peened over edges of said lug, the edges of said side walls being peened over the outer edges of said tying member.

5. In an elastic fiuid turbine, a rotor having a row of buckets mounted thereon, each of said buckets having an integral cover portion, the cover portions of adjacent buckets substantially abutting against each other and spacing the outer ends of said buckets apart, a slot in the upper surface of each of said cover portions, the slots being so aligned as to form a continuous circumferential slot around the periphery of said row of buckets, the side walls of said slots having overhanging beads, rectangular lugs integral with said cover portions extending upwardly from the bottom of said slot and centrally disposed therein with respect to said side walls, a pair of tying members for securing a plurality of adjacent bucket covers together, said tying members each being perforated along one edge for cooperatively fitting around said rectangular lugs, the other edge of each of said tie members adapted to cooperatively fit under the overhanging bead of said side wall, said tying members being secured in said slot against the base'thereof by peened over edges of said lugs and said o erhanging beads.

6. An elastic fluid turbine bucket having an individual cover portion integral with the upper end thereof, a slot provided in the upper surface of said cover portion adapted to receive a member for tying a plurality of similar buckets together, the upper edges of the slot side walls being provided with overhanging beads, a centrally disposed lug extending upwardly from the base of said slot and spaced from the opposite side walls thereof, the overhanging beads and the upper edges of said lug adapted to be deformed to rigidly secure a tying member against the base of said slot.

i ARTHUR R. SMITH. 

